The present invention relates generally to fluidic damping devices and more particularly to a fluid damping unit which may be utilized either as a shock absorber or as a telescopic strut.
Devices of the type to which the present invention relates usually comprise a cylinder, a piston rod inserted into the cylinder from an end thereof through a guiding and sealing unit, and a piston which is fastened to the piston rod near the inner end of the piston rod and which divides the interior of the cylinder into two work chambers, namely an annular work chamber which borders the guiding and sealing unit, and a work chamber at the bottom of the cylinder which borders that end thereof which is located opposite the guiding and sealing unit. A fluid charge is provided in the cylinder and, in the case where a liquid charge is utilized, a compensating volume bordering the liquid charge is provided. The piston rod is arranged to be moved reciprocally between an inner end position, in which the rod is retracted in the cylinder to the extent possible, and an outer end position in which the rod is fully extended out of the cylinder. In the operation of such a device, a damping effect is produced, beginning at a predetermined intermediate position between the inner end position and the outer end position, as a result of increased resistance created by a pull stopping unit accommodated in the annular work chamber which counteracts the movement of the piston rod out of the cylinder in the direction toward the outer end position.
The term "pull stopping unit" derives from the fact that this unit is effective as a stop device or as a brake, when the cylinder is held stationary and the piston rod is pulled out of the cylinder.
Such a fluid damped unit is known from German Utility Model No. 6,901,747. In the known unit, increase of the resistance to movement of the piston rod when it is approaching the outer end position results exclusively from a mechanical spring which is compressed during this approach movement between a sealing and guiding unit, on the one hand, and the piston rod, on the other hand.
The invention is directed to the task of providing an improved fluid damped unit of the aforementioned type which will effect braking of the piston rod as smoothly and quietly as possible during the approach of the piston rod to the outer end position, and which will do so under different operating conditions including the case involving a slow extending movement of the piston rod as well as in the case involving a quick extending movement of the piston rod.
The indicated results are achieved, according to the invention, in that an increase in the resistance is obtained by utilization of a mechanical spring action as well as of a fluidic throttling action of the pull stopping unit.